System and method for determining level and density distribution

1. A radar level gauge system for determining a level of an interface between liquid phase product and vapor phase product in a tank, and a density distribution in said liquid phase product, said radar level gauge system comprising: a first transceiver for generating, transmitting and receiving electromagnetic signals having a first set of signal properties; a second transceiver for generating, transmitting and receiving electromagnetic signals having a second set of signal properties different from said first set of signal properties; an antenna coupled to said first transceiver and to said second transceiver, said antenna being arranged to radiate an electromagnetic first transmit signal having said first set of signal properties, and an electromagnetic second transmit signal having said second set of signal properties, and to receive a first reflection signal resulting from reflection of the first transmit signal and a second reflection signal resulting from reflection of the second transmit signal; a tubular waveguide extending from a top of the tank towards a bottom of the tank, said tubular waveguide being arranged and configured to guide said first transmit signal and said second transmit signal radiated by said antenna towards said interface between liquid phase product and vapor phase product and into said liquid phase product, and to guide said first reflection signal and said second reflection signal back towards said antenna; at least a first plurality of signal interacting structures arranged at different levels along a first segment of said tubular waveguide, each signal interacting structure in said first plurality of signal interacting structures being configured to selectively interact with said second transmit signal to contribute to said second reflection signal; and processing circuitry connected to said first transceiver and said second transceiver, said processing circuitry being configured to determine said level of the interface between liquid phase product and vapor phase product based on a relation between said first transmit signal and said first reflection signal, and said density distribution in said liquid phase product based on a relation between said second transmit signal and said second reflection signal, wherein each signal interacting structure in said first plurality of signal interacting structures is a reflecting structure arranged and configured to exhibit a first reflection coefficient for said first transmit signal and a second reflection coefficient for said second transmit signal, a ratio between said first reflection coefficient and said second reflection coefficient being less than 1:2, and wherein said processing circuitry is configured to determine: a first measure indicative of a distance between a first signal interacting structure and a second signal interacting structure in said first plurality of signal interacting structures based on a relation between said second transmit signal and said second reflection signal; a second measure indicative of a distance between a third signal interacting structure and a fourth signal interacting structure in said first plurality of signal interacting structures based on a relation between said second transmit signal and said second reflection signal; a first average density for a first level range in said tank based on said first measure; and a second average density for a second level range in said tank based on said second measure.

2. The radar level gauge system according to claim 1 , wherein said first plurality of signal interacting structures comprises at least three signal interacting structures, mutually spaced apart along the first segment of said tubular waveguide.

3. The radar level gauge system according to claim 1 , wherein said first set of signal properties comprises a first polarization, and said second set of signal properties comprises a second polarization, different from said first polarization.

4. The radar level gauge system according to claim 3 , wherein said first polarization is a first linear polarization, and said second polarization is a second linear polarization, orthogonal to said first linear polarization.

5. The radar level gauge system according to claim 1 , wherein said first set of signal properties comprises a first propagation mode, and said second set of signal properties comprises a second propagation mode, different from said first propagation mode.

6. A radar level gauge system for determining a level of an interface between liquid phase product and vapor phase product in a tank, and a density distribution in said liquid phase product, said radar level gauge system comprising: a first transceiver for generating, transmitting and receiving electromagnetic signals having a first set of signal properties; a second transceiver for generating, transmitting and receiving electromagnetic signals having a second set of signal properties different from said first set of signal properties; an antenna coupled to said first transceiver and to said second transceiver, said antenna being arranged to radiate an electromagnetic first transmit signal having said first set of signal properties, and an electromagnetic second transmit signal having said second set of signal properties, and to receive a first reflection signal resulting from reflection of the first transmit signal and a second reflection signal resulting from reflection of the second transmit signal; a tubular waveguide extending from a top of the tank towards a bottom of the tank, said tubular waveguide being arranged and configured to guide said first transmit signal and said second transmit signal radiated by said antenna towards said interface between liquid phase product and vapor phase product and into said liquid phase product, and to guide said first reflection signal and said second reflection signal back towards said antenna; at least a first plurality of signal interacting structures arranged at different levels along a first segment of said tubular waveguide, each signal interacting structure in said first plurality of signal interacting structures being configured to selectively interact with said second transmit signal to contribute to said second reflection signal; and processing circuitry connected to said first transceiver and said second transceiver, said processing circuitry being configured to determine said level of the interface between liquid phase product and vapor phase product based on a relation between said first transmit signal and said first reflection signal, and said density distribution in said liquid phase product based on a relation between said second transmit signal and said second reflection signal wherein: said radar level gauge system further comprises a second plurality of signal interacting structures arranged at different levels along a second segment of said tubular waveguide different from said first segment, each signal interacting structure in said second plurality of signal interacting structures being configured to selectively interact with said first transmit signal to contribute to said first reflection signal; and said processing circuitry is configured to: determine, for levels along said first segment of said tubular waveguide, said level of the interface between liquid phase product and vapor phase product based on a relation between said first transmit signal and said first reflection signal, and said density distribution in said liquid phase product based on said second reflection signal along said first segment of said tubular waveguide and based on said first reflection signal along said second segment of said tubular waveguide; and determine, for levels along said second segment of said tubular waveguide, said level of the interface between liquid phase product and vapor phase product based on a relation between said second transmit signal and said second reflection signal, and said density distribution in said liquid phase product based on said first reflection signal along said second segment of said tubular waveguide.

7. A method of determining a level of an interface between liquid phase product and vapor phase product in a tank, and a density distribution in said liquid phase product, using a radar level gauge system comprising: a first transceiver; a second transceiver; an antenna coupled to said first transceiver and to said second transceiver; a tubular waveguide extending from a top of the tank towards a bottom of the tank; at least a first plurality of signal interacting structures arranged at different levels along a first segment of said tubular waveguide, each signal interacting structure in said first plurality of signal interacting structures being configured to selectively interact with electromagnetic signals having a given set of signal properties; and processing circuitry connected to said first transceiver and said second transceiver, said method comprising the steps of: transmitting, by said first transceiver, an electromagnetic first transmit signal having a first set of signal properties, different from said given set of signal properties; transmitting, by said second transceiver, an electromagnetic second transmit signal having a second set of signal properties, constituting said given set of signal properties; radiating, by said antenna, said first transmit signal and said second transmit signal into said tubular waveguide; receiving, by said antenna, an electromagnetic first reflection signal resulting from reflection of said first transmit signal, and an electromagnetic second reflection signal resulting from reflection of said second transmit signal; determining, by said processing circuitry, said level of the interface between liquid phase product and vapor phase product based on a relation between said first transmit signal and said first reflection signal; determining a first measure indicative of a distance between a first signal interacting structure and a second signal interacting structure in said first plurality of signal interacting structures based on a relation between said second transmit signal and said second reflection signal; determining a second measure indicative of a distance between a third signal interacting structure and a fourth signal interacting structure in said first plurality of signal interacting structures based on a relation between said second transmit signal and said second reflection signal; determining a first average density for a first level range in said tank based on said first measure; and determining a second average density for a second level range in said tank based on said second measure.